Multi-instancing migration (Step 8 — forcing function): delete the static BattleRecoveryInfo
fallback the earlier .ambient-recoveryinfo patch added as a coexistence shim. BattleRecoveryInfo
is now strictly per-session ambient. Supersedes the intermediate .ambient-recoveryinfo patch
(kept for the audit trail).

Semantics:
  - BattleRecoveryInfo (getter) : Current?.RecoveryInfo — soft (null when no scope). The
    MulliganMgrBase.StartDeal call site reads this with a null-tolerant pattern, so a null
    degrade is the historical fallback. Inside a scope, returns the per-session RecoveryInfo
    (SessionBattleEngine pre-seeds an uninitialized BattleRecoveryInfo on its ctx field
    initializer).
  - BattleRecoveryInfo (setter) : BattleAmbient.Require().RecoveryInfo = value — strict
    (writes must land on the per-session ctx; forcing function).

Related (SVSim.BattleNode/Sessions/Engine/EngineGlobalInit.cs): the dead `Data.BattleRecoveryInfo
= ...` write inside the `_done` lock block is also deleted (flagged by Task 7 reviewer). The
per-session ctx pre-seeds RecoveryInfo, so the process-global write was dead the moment the
ambient seam landed.

In-file edits:
  - line ~179  declaration `private static BattleRecoveryInfo _battleRecoveryInfoFallback;`  DELETED
  - lines ~180-189  the ambient+fallback get/set body  REPLACED with strict semantics

--- Engine/Wizard/Data.cs  (~lines 179-189)
-	private static BattleRecoveryInfo _battleRecoveryInfoFallback;
 	public static BattleRecoveryInfo BattleRecoveryInfo
 	{
-		get => SVSim.BattleEngine.Ambient.BattleAmbient.Current?.RecoveryInfo ?? _battleRecoveryInfoFallback;
-		set
-		{
-			var c = SVSim.BattleEngine.Ambient.BattleAmbient.Current;
-			if (c != null) c.RecoveryInfo = value;
-			else _battleRecoveryInfoFallback = value;
-		}
+		// Soft read: returns null when no scope is active. The MulliganMgrBase.StartDeal call site
+		// reads this with a null-tolerant ??=-style pattern, so a null degrade is the historical
+		// fallback. Inside a scope, returns the per-session RecoveryInfo (SessionBattleEngine
+		// pre-seeds an uninitialized BattleRecoveryInfo on its ctx field initializer).
+		get => SVSim.BattleEngine.Ambient.BattleAmbient.Current?.RecoveryInfo;
+		// Strict setter: writes must land on the per-session ctx. No historical production caller
+		// writes this outside a scope; an unwrapped write now fails fast (forcing function).
+		set => SVSim.BattleEngine.Ambient.BattleAmbient.Require().RecoveryInfo = value;
 	}